TIDES

Question 1

what are tides?

Answer 1

• waves
• exact form of tidal record varies with location

Question 2

how are tides created?

Answer 2

• gravitational attractive force acts as centripetal force tht keeps earth and moon in mutual orbit around common centre of mass

Question 3

does the magnitude of force vary with distance?

Answer 3

yes

Question 4

consider magnitude of force for unit mass at three locations?

Answer 4

1. on earths surface directly beneath moon
2. at centre of earth
3. on earths surface on opposite side to moon

Question 5

what does the equilibrium tidal theory consider?

Answer 5

• spherical earth covered with uniform ocean
• action of gravitational force on fluid elements in ocean

Question 6

what is tidal generating force (TGF)?

Answer 6

• net force acting on a fluid element

Question 7

how to calculate TGF?

Answer 7

mass of tide raising body/ distance to tide raising body ^3

Question 8

how are tidal bulges formed?

Answer 8

• TGF causes movement of water
• two bulges of water on opposite sides of the earth
• aligned with the tide raising body

Question 9

how are diurnal/ semidiurnal tides created?

Answer 9

• earth spins on axis once per day
• points on the surface move beneath tidal bulges
• form of tide depends on latitude and lunar declination

Question 10

what is lunar declination?

Answer 10

• angle of moons orbit with equator

Question 11

tidal periods?

Answer 11

suggested = 24 HOURS (D) 12 HOURS (SD)
OBSERVED = 25H50M (D) 12H25M (SD)

Question 12

what tide does moon affect?

Answer 12

lunar tide

Question 13

what tide does sun affect?

Answer 13

solar tide

Question 14

what is the spring neap cycle?

Answer 14

• considers co- occurrence of lunar and solar tides
• tow sets of tidal bulges. one with moon one with sun
• overall tide is superposition of both tides = depends on alignment of earth, moon and sun

Question 15

timing of spring neap cycle?

Answer 15

• fortnight cycle of tidal variations

Question 16

spring tides simplified

Answer 16

1. sun earth and moon make straight line in space
2. new moon or full moon
3. tidal bulges add together
4. higher HW and lower LW
   = increased tidal range

Question 17

neap tides simplified?

Answer 17

1. sun, earth, and moon make right angle in space
2. first quarter or third quarter
3. third bulges work in opposition
4. lower HW and higher LW
5. decreased tidal range

Question 18

factors of equilibrium tidal theory?

Answer 18

• explains origin of tides
• correctly predicts key features
• cannot capture details of real tides

Question 19

factors of dynamic tidal theory?

Answer 19

• constraining influence of land masses
• frictional influence of rotating earth
• deflection of flows by coriolis effect

Question 20

what is the rotary tidal systems?

Answer 20

ASSUME CLOUD BASIN IN NORTHERN HEMISPHERE
- water flowing in basin deflects to right and hugs coast
HW travels counter- clockwise around basin
- maximum tidal range at coast
- minimum tidal range in centre
= rotary wave (kelvin wave)
= amphidromic system

Question 21

what can amphidromic systems do?

Answer 21

• create maps summarising tidal variations in a region

Question 22

how do you create a map summarising tidal variations?

Answer 22

1. draw lines joining locations of equal tidal phase
   - where HW occurs at the same time
   - COTIDAL or COPHASE lines
2. draw lines joining locations of equal tidal range
   - CORANGE lines

Question 23

what is the central (nodal) point called?

Answer 23

• amphidromic point